The present invention is directed to a circuit interrupter using dielectric liquid with energy storage.
Liquified gas circuit interrupters are well-known one being disclosed in U.S. Pat. No. 3,150,245 to W. M. Leeds et al. as inventors. Leeds discloses a fluid such as sulphur hexafluoride and provides driving means for forcing the liquified gas at high pressure toward the arc zone when the contacts of the interrupter are parted. One of the problems pointed out in Leeds is maintaining a high enough pressure especially during the low temperature ambient operation for effective arc extinguishing. In order to maintain an adequate injection pressure, Leeds proposes three techniques which are (1) the use of a mechanically operated impulse device, (2) the use of an accumulator with gas such as nitrogen in one end and sulphur hexachloride in the other, and (3) the use of sulphur hexachloride and a heater to maintain a high enough temperature.
A problem with the Leeds design is the remarkable rise in the fault current interrupting requirements in the past decade. For example, Leeds is directed to interrupting perhaps 50,000 amperes with pressures which are generally less than 1,000 psi. In contrast with a current of for example 120,000 amperes, as much as 2,000 psi may be required. With the required high pressure two problems are presented. One is that when an arc is formed upon separation of the contacts the arc in essence shuts off the flow of interrupting fluid and causes an incipient high pressure maximum. This pressure may be much higher in fact than the required arc extinguishing pressure and subjects the entire interrupter device to severe mechanical stress. On the other hand, when the arc is near current zero, the arc diameter reduces thus allowing the liquid to flow out the orifices more rapidly. This tends to reduce the pressure below an acceptable level in which an arc might be re-established. In other words, a low pressure minimum may be produced by rapidly increasing flow area while the pump has a slow response to these changing conditions.
Fischer U.S. Pat. No. 3,406,269 discloses in FIGS. 5 and 6 techniques (including an accumulator) for maintaining sufficient pressures. However, since the systems are closed there is no pressure minimum problem.